1. Field of Inventions
The present inventions relate generally to medical devices that support one or more diagnostic or therapeutic elements in contact with body tissue.
2. Description of the Related Art
There are many instances where diagnostic and therapeutic elements must be inserted into the body. One instance involves the treatment of cardiac conditions such as atrial fibrillation and atrial flutter which lead to an unpleasant, irregular heart beat, called arrhythmia.
Normal sinus rhythm of the heart begins with the sinoatrial node (or xe2x80x9cSA nodexe2x80x9d) generating an electrical impulse. The impulse usually propagates uniformly across the right and left atria and the atrial septum to the atrioventricular node (or xe2x80x9cAV nodexe2x80x9d). This propagation causes the atria to contract in an organized way to transport blood from the atria to the ventricles, and to provide timed stimulation of the ventricles. The AV node regulates the propagation delay to the atrioventricular bundle (or xe2x80x9cHISxe2x80x9d bundle). This coordination of the electrical activity of the heart causes atrial systole during ventricular diastole. This, in turn, improves the mechanical function of the heart. Atrial fibrillation occurs when anatomical obstacles in the heart disrupt the normally uniform propagation of electrical impulses in the atria. These anatomical obstacles (called xe2x80x9cconduction blocksxe2x80x9d) can cause the electrical impulse to degenerate into several circular wavelets that circulate about the obstacles. These wavelets, called xe2x80x9creentry circuits,xe2x80x9d disrupt the normally uniform activation of the left and right atria.
Because of a loss of atrioventricular synchrony, the people who suffer from atrial fibrillation and flutter also suffer the consequences of impaired hemodynamics and loss of cardiac efficiency. They are also at greater risk of stroke and other thromboembolic complications because of loss of effective contraction and atrial stasis.
One surgical method of treating atrial fibrillation by interrupting pathways for reentry circuits is the so-called xe2x80x9cmaze procedurexe2x80x9d which relies on a prescribed pattern of incisions to anatomically create a convoluted path, or maze, for electrical propagation within the left and right atria. The incisions direct the electrical impulse from the SA node along a specified route through all regions of both atria, causing uniform contraction required for normal atrial transport function. The incisions finally direct the impulse to the AV node to activate the ventricles, restoring normal atrioventricular synchrony. The incisions are also carefully placed to interrupt the conduction routes of the most common reentry circuits. The maze procedure has been found very effective in curing atrial fibrillation. However, the maze procedure is technically difficult to do. It also requires open heart surgery and is very expensive.
Maze-like procedures have also been developed utilizing catheters which can form lesions on the endocardium to effectively create a maze for electrical conduction in a predetermined path. The formation of these lesions by soft tissue coagulation (also referred to as xe2x80x9cablationxe2x80x9d) can provide the same therapeutic benefits that the complex incision patterns that the surgical maze procedure presently provides, but without invasive, open heart surgery.
Catheters used to create lesions typically include a relatively long and flexible body portion that supports a soft tissue coagulation electrode on its distal end and/or a series of spaced soft tissue coagulation electrodes near the distal end. The portion of the catheter body that is inserted into the patient is typically from 23 to 55 inches in length and there may be another 8 to 15 inches, including a handle having steering controls, outside the patient. The length and flexibility of the catheter body allow the catheter to be inserted into a main vein or artery (typically the femoral artery), directed into the interior of the heart, and then manipulated such that the coagulation electrodes contact the tissue that is to be ablated. Fluoroscopic imaging is used to provide the physician with a visual indication of the location of the catheter.
Therapeutic lesions, whether formed alone or as part of a therapeutic lesion pattern, must often be formed in varying lengths to suit particular situations. In those instances where the catheter includes a single tip electrode, the physician must manipulate the catheter so that the tip electrode is dragged along the desired length of tissue during lesion formation. Such a technique is problematic because it is difficult to properly execute and often results in incomplete lesions, lesion gaps and tissue charring. Superior results have been obtained using catheters that support multiple electrodes. Here, some or all of the electrodes on the catheter may be selectively connected to an energy source to produce lesions of various lengths. The inventors herein have determined that, while superior to the drag technique, forming lesions of various lengths with conventional multiple electrode catheters can be inconvenient because such catheters require the use of a power supply and control device that is capable of selectively connecting some or all of the electrodes to the energy source.
An apparatus in accordance with one embodiment of one present invention includes a support structure, a plurality of longitudinally spaced conductive regions, and an actuation device including at least one electrical contact located within the support structure and movable between respective positions where the electrical contact is in electrical connection with a respective conductive region.
Such an apparatus provides a number of advantages over conventional apparatus. For example, lesions of various lengths and configurations may be produced by forming a portion of an overall lesion when the actuation device is in one position, then moving the actuation device to another position to form an additional portion of the lesion, and so on until the desired lesion is formed. As a result, the apparatus allows physicians to selectively actuate some or all of the conductive regions to form a variety of lesions without having to use a power supply and control device that is itself capable of selectively connecting some or all of the conductive regions to an energy source. Additionally, because such an apparatus also allows lesions of varying length to be created without moving the support structure, the precise positioning of the apparatus will not be compromised and the unintended ablation of non-target tissue will be prevented.
The above described and many other features and attendant advantages of the present inventions will become apparent as the inventions become better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings.